Method of manufacture of hollow floats of thin metal for ship compasses



y 1950 J. M. s. KAUFMAN AL 2,505,776

METHOD OF MANUFACTURE OF HO W FLOATS OF THIN METAL FOR SHIP COMPASSES Original Filed July 11, 1941 2 Sheets-Sheet l.

May 2, 1950 J. M. s. KAUFMAN ETAL 2,505,776

METHOD OF MANUFACTURE OF HOLLOW FLOATS OF THIN METAL FOR SHIP COMPASSES Original Filed July 11, 1941 2 Sheets-Sheet 2 Jae A1. 5. hm 19% eZZey zfiwawzzf Show Patented ay 2, 1950 UITED STATES PATENT OFFICE METHOD OF MANUFACTURE OF HOLLOW FLOATS F THIN METAL FOR SHIP COM- PASSES Original application July 11, 1941, Serial No.

402,030. Divided and this application September 30, 1944, Serial No. 556,582

1 Claim.

This invention relates to methods of providing corrosion resisting components for magnetic compasses of the type ordinarily used on ships. The invention is particularly drawn to such magnetic instruments as are used in the presence of corrosive fluid, which fluid may be either air having corrosive constituents, or liquid contained within the bowl forming the outer casing of the said compass.

It is an object of the invention to teach methods of providing corrosion resisting surfaces which may be easily and economically applied, which surfaces will afterwards permit repair with facility, will avoid any magnetic diificulties and will provide a pleasant dull surface of non-glaring quality, resembling white paint.

It is a further object of the invention to provide a superior corrosion resisting base for paint to be applied under corrosive conditions. It is a further object of the invention to provide methods for coating the thin float portions of mag netic compasses in such a manner as to avoid development of undesired strain during the coating operation. It is a further object of the invention to perfect the corrosion-resistant properties of such compasses and to correct any injuries done by abrasion or otherwise.

While a specific type of liquid-filled compass is described herein, it will be understood that the same type of construction may be applied under other conditions where corrosion exists. Such mode of fabrication may also be employed wherever it is desired to apply paint to metallic surfaces to obtain good bonding.

Such techniques may also be applied to any other objects which are fabricated of separate soldered parts, which are required to be either leakproof or corrosion-proof, or to have an attractive non-glare surface. Further still, the technique described herein may be applied to magnet materials of any nature or of any shape although it is particularly applicable to those having a significant aluminum content. Such materials may be utilized either inside or outside of magnetic indicating instruments and may be employed in electromagnetic or magnetic devices of any type where corrosive conditions are found.

Other objects and advantages of the invention will be evident from the following drawings in which:

Figure 1 indicates a general cross-sectional view of an instrument constructed according to the invention.

Figure 2 shows a top view of an instrument such as shown in Figure 1.

Figure 3 shows the bottom view of the moving system of this instrument.

Figure 4 shows a portion of the dial of the instrument as shown in Figure 3.

Figure 5 shows a crosssectional view of a portion of the dial shown in Figure 4, taken across the line 5-5.

Figure 6 shows the method of plating the moving system shown in Figure 3.

Figure 7 shows the process of plating a. bowl such as that employed in the instrument shown in Figure 1.

Figure 8 shows a longitudinal cross-sectional view of a cylindrical bar magnet plated according to the method of the invention.

Figure 9 shows another type of magnet plated according to the method of the invention.

Referring now to Figure 1, I shows the outer casing or bowl of a compass which is ordinarily used for steering ships and boats. This bowl is covered with a transparent cover 2. At the sides of the bowl I are knife edges 3, 3, upon which the entire compass rests. At the lower part of the bowl I is an expansion chamber usually made of corrugated metal and represented as i. The com: pass is closed at the bottom by a cover which may or may not be transparent and is designated as 5. Within the bowl is a pivot support ii, upon which rests a pivot 1. Upon this pivot, mounted so as to be free to rotate about any axis, is the moving system 8. This moving system isordi-, narily observable through the top of the glass cover 2, and has mounted upon it magnets 9, 9. and I0, H), which orient it in the direction of the magnetic meridian.

The moving system 8 is more fully shown in Figure 3. Here a dial is represented as It. This dial is in the form of a rim of metal, which is formed with overhanging portions so as to stiiien it. It is fastened by means of channel shaped members or tubes 15, to a float assembly indicated as H.

In Figures 1 and 3, the outer dial, the connecting tubes or channels l5, and the float member ll, composed of an upper part and a lower part are shown. Fastened to the bottom of the float I I, in adjustable fashion are magnets 9, 9, and 10, I0. These are held by clamps l3, l3, so as to be movable over a limited range and to allow orienting the magnets 9, 9, and ll], [0, to obtain the correct setting of the card relative to the magnetic meridian.

With these clamps the magnets may be moved forward or backward to balance the card in the direction of their length. They may also be ,able corrosive properties, tecting coating willsufienextreme corrosion if 3 shifted bodily sidewise, or may be twisted slightly. Thus, by moving the clamps and shifting the magnets, one can balance the card and magnet assemblyand can also orient the magnetic axis so that it coincides with the geometric northsouth axis of the moving system.

A portion of the card o dial it is shown in Figure 5. Here the lines and numerals are shown as being out completely through the metal'so'as' to be permanent and inefiaceable. If the card is illuminated from below, these figures and lines appear especially distinct. Alternatively, the lines and numerals cut through. the metal maybe filled either with a paint or with a luminous material, thus providing a firm bond and an accurate 5 location for the paint.

In use the bowl shown in Figure l ordinarily filled with liquid it. This is often a mixture of alcohol and water, which has intrinsic unavoidplaced in this liquid. Where the liquid. is-omitted iromthe bowlg-theair itself, especially in marine atmospheres, may have considerable corroding power. All parts 01"; and especially the interior of the bowl l must therefore be protected against COIIOSlOn.

Furthermore,'sincereadings are to'be made and since the illumination availableis often weak, the interio rof the bowl should be a t color. Fur-ther still, because sun occasionally shines upon the compass, it is necessary that the interior beofa non-glaring nature. ln the normal use oi. the-compass, it is often mounted ina binnacle which serves tosu-pport it and also to provide illumination. This illumination often turnished -by-a light above or below the In -either case, th light will introduce "-lare if any brightly reflecting surfaces are present in the -compass.

Various attempts have been made to meet the problems involved. @neexpedient which has been =tried has been the use of hottin applied in molten -=-f-ormto the interior oi'the bowl I. The expansion chamber l, made of this metal.--usually brass-- and previously tinned in the same --manner, =1's thensoldered to the bottom part of the'bowl. Afterthe assembly is thus made, the i'nterior of 't-he bowl is painted, usually with-an albumin-and white lead we; is supported. to resist th'e' action of alcohol. This construction is highly --unsatisia'ctory in service. The long so ldered seam between the expansion chamber and-thebottomof the bowl 5 often develops-pin holes, which are due to solder-not-being perfectly adherent to thetwo members. Furthermore, the interior surfaces of the bowl i, being smooth-as customarily-obtained with hot tin, do not pro- -v-ide a-very good bond for paint, which adheres best to ough surfaces. Further still, the paint is -rather difiicult to apply and often despite the best efiorts of the maker will prove unsatisiactory'in :appearance and durability. itwill oitenachip off or-sca'le, and will in any event, turn yelloivwvith -age. Repair of the paint is often diificult, in many -cases -involving the removal of :all the-old. paint from the interior of the bowl, in which process chipping-orscraping is often resorted to.

In an etlortto avoid these diificulties, chromium plating hasbeen tried for the interiorof the bowl. brought about conditions which-were even worse than those sought to be corrected. The chromium, requiring a plating of nickel under- -'--neath, showed undesirable magnetic properties v-whichintroduced serious errors in the compass.-

Metals without pro- Furthermore, the chromium provided a glaring surface uncomfortable to the observer. The

. chromium, moreover, developed serious corrosion.

.In the case of .the element shown in Figure 3, the white paint proved to be highly unsuitable. First, it would tend to fill the graduations such as shown in Figure 5, which was undesirable when ,-it was required to have light pass therethrough. When paint was applied to the outside of the float I I, it was foundthat the extreme flexibility of this :mernber and; its fbreathing with temperature changes, caused the brittle albumin paint to crack --andscale ofi.

Ghromium-was tried here also with poor results. Magnetic dificulties arose which made virtually impossible the correct setting of the magnectic; system. Further still, corrosion developed and the moving system had a glaring aspect which was very uncomfortable to the eyes of the observer.

-Attempts were made to coat the magnetsfl, 9 and lily-IE3, which are made of Alnico magnet -rnaterial, with-chromium. This proved unsuccessiul, it'being absolutely impossible to plate'the magnets with chromium. Further still, the chromium coating, or whatever of it adhered to the A121iC0,"W0'llZd serve-toaccelerate corrosion, rather than retard it.

Where reference is made to Alnico herein,itis intended to-cover the alloys known in the trade bythisname. Suchalloys maycontainas an example; approximately '10 per centaluminum; 17 percent nickel; 12.5 percent cobalt; 6 per cent copper; balance, iron. Qther compositions varydug-somewhat from the-proportions given, come under the trade term-of"-Alnico.

Coating-the magnet wit-h'some such material as brass was-nextresorted to. In one case this was *accomplisl1ed b-yputting-a sheath of thin sheet rass about the'mag-neuand soldering the seam along the length of the magnet and further sol- -dering theen'd'shut. In other cases, the magnets were insertedin brass tubes and the ends sealed with-soldered'brasscaps or-with solder alone. The latterexpedient added-too much weight to the magnet, so that 'theformer'expedient was more frequently resorted to.

The modeof'constructiondesoribed' proved expensive and unsatisfactory, involving soldering a considerable length 'of 'joint, and providing "a structure'which was highly vulnerable to leaks developed-by pin" holes. Moreover, the'sheaths or tubes placed 'about'the magnets "added to the weight and bulk of themoving'system, an undesirable feature from the pointer view'of speed of operation of the moving system.

'In the presentinvention the 'following procedure is followed in order't-oiabricate the'bowl I. 'Su'cha-bowlis often made ofbronze, brass, coppehior someothernon magneticmaterial. To thetbottom of this bowl is then soldered the "ex"- pansion chamber or "capsule 4,, the joint' -being ,ma'de'with ordinary soit solder "made of tin and lead. Theinteriorof-the bowl is next covered electrolyticallywith-a deposit of tin l'l,-applied me. mannenwhich will 'be'hereinafter described. Thecoating of tin isapplied simultaneously to 'thainterior'of the expansion chamber, the interioroi the bowl, and to-all of the soldered joints. Tin is particularly beneficial for this purpose, since in theprcper-sort of bath it has great throwing power. Thus, it willseek out and cover-minute crevices, porous spots, small holes, etc. "Ifany such porous or open spots exist in the casing, providing they are not too'large, they will be sealed effectively by the tin coating. The same applies to any defects which may exist in the soldered joints between the expansion capsule i, and the bowl 5, or indeed between the parts of the expansion capsule itself.

It is to be emphasized here that the beneficial effects of using tin for the various parts of the compass arise from its application by electrolytic deposition from the proper sort of solution. In the case of the magnets, since these are often provided in rough cast form, they will have a number of deep pits and blow-holes. The tin will throw or deposit in these cavities, preventng the opportunities for later corrosion, which would be observed with other types of plating.

In the case of the interior of the bowl, here also, one usually uses a cast bowl and although this is often machined on the interior, there will be the inevitable porous spots and blow-holes in the interior surface. Here also, tin deposited properly will protect the metal in these cavities and prevent later corrosion therein. Further still, the interior of the bowl is of complicated shape and has re-entrant surfaces, particularly in the interior of the expansion chamber. Because of the extreme throwing power in the technique described, the tin will be deposited in ample quantity on all the surfaces in one simple operation.

In the case of the card assembly, referred to below, it will be seen that there also, there are a number of re-entrant surfaces and cavities which will be properly plated due to the throwing power of the tin. Furthermore, the plating of the assembled moving system hereinafter described, is possible because of the throwing power of the tin in the bath described. Were other materials or other techniques to be utilized, the plating of the assembled piece would be futile, since it would be impossible to obtain deposition of metal in the many crevices present in an assembled piece, and it is precisely in these crevices that the coating previously applied is most apt to be abraded and to require protection.

The coating of tin applied in the manner taught herein is crystalline in nature. When viewed with the naked eye, such a surface appears a dull grayish white, giving a pleasing appearance resembling dull white paint. Such a surface is entirely suitable for use, without any further coating. However, Where paint is desired, it can be applied to the interior of the bowl I after the crystalline deposit of tin has been placed. This crystalline deposit, being formed of minute particles or minute crystals of tin, provides a roughened surface to which paint adheres better than to the smooth surface left by hot tinning.

A suitable coating for the interior of the compass bowl is a paint made with vinyl resin. This can be made white with some pigment such as a titanium oxide, and after application and drying will be found to resist the solvent action of alcohol and water. It will also resist the solvent action of other organic liquids which may be used as the compass fluid. Alternatively, the vinyl resin may be formed in the shape of a liner and pressed into the interior of the bowl. A white paint made with vinyl resin may also be applied to the moving system. This paint may be made very thin in contradistinction to the albumin paint previously used. The latter had to be used in thickened form. The paint made with vinyl resin may be so thin that it will not fill any graduations which are cut through the moving system. The vinyl resin paint need not have any great covering power, since the undercoat of crystalline tin has a whitish color.

In the case of the moving system, such as shown in Figure 3, the dull or crystalline tin provides a particularly efiective coating for such a member as shown in detail in Figure 5. Because of the throwing power of the tin, the vertical wall left by cutting away the metal will be effectively coated and will resist corrosion. Furthermore, the surface of the dial will have a particularly pleasing dull appearance, such as described before for the interior of the bowl. The float portion H, coated in the same way, will have the same corrosion resistance as described before and will present the same pleasing grayish-white appearance. The coating has particular advantages when applied to magnets such as 9, 9, and Ill, I0. I

The coating of Alnico magnet material with a corrosion resistant material has proved to be a particularly vexing problem. Because of the solvent eifect of the alcohol-water mixture customarily used, ordinary varnishes and paints are not suitable. The expedient of coating the magnet with a thin sheath or covering of brass having solderedjoints has been used. This has disadvantages which have been enumerated above. Plating withvarious metals has also been tried and has heretofore been found highly unsuccessful. It appears that the aluminum in the Alnico alloy forms a chemical coating thereon which prevents the adherence of plated metal.

It has been discovered, however, that tin, when used electrolytically in a highly alkaline bath, in the manner described herein, will coat Alnico properly, so as to make it completely resistant to corrosion. The tin appears to adhere well and to fill the crevices and pores which are often present in cast Alnico material. Tests on immersion of such magnets in solutions having different corrosive properties, such as salt water, pure alcohol, and mixtures of alcohol and water, all show that the tin provides an adequate and satisfactory corrosion resistant coating.

A satisfactory plating bath for the Alnico magnet material can be prepared as follows:

To one gallon of water is added 16 ounces of sodium stannate, one ounce of sodium hydroxide, two ounces of sodium acetate, approximately of an ounce of fresh hydrogen peroxide, and about of an ounce of borax. Heat is applied to bring the bath to a temperature of about F. A voltage of about 6 volts is applied, and a current density of about 3.0 amperes per square foot of surface area being plated. The anode should not be of too large area and should be of such area that the current density at the anode is about 3.0 amperes per square foot. It is necessary that the current density figure herewith be utilized, since part of the success of the plating operation depends upon this.

Before plating the Alnico magnet material, it

should be ground on some sort of abrasive wheel to remove most of the scale and surface dirt. It is then cleaned with pumice, preferably in a paste made with water. Contrary to the practice usually followed in plating, it has been found best to avoid a chemical cleaning treatment for this material.

The plating technique, namely the cleaning with pumice and water, and the composition and other details concerning the plating bath may also be followed for the plating of brass, bronze, or copper parts to be used in the construction of 7.5 a compass. For the other parts of the compass described hereimit is understood that the mode Ofplating will be substantially the same as that described for the plating technique of the Alnico magnet material.

The plating technique described herein may be modified and other means used to obtain the same result. The specific method and composition of the bath disclosed is intended to serve as an example :by which successful results may be obtained.

Figure 8 shows a longitudinal cross-sectional view of a cylindrical Alnico magnet 9 covered with anelectroplated coating of tin l3.

:Figure 9 shows a cross-sectional view of a horseshoe type of magnet l9- also made of Alnico and also covered with a coating of tn 2%. A precaution desirable in the plating of magnets isrthat they bezplated in the unmagnetized condition. .Magnetized material will pick up small pieces of iron and steel, which will project through-the plating and subsequently corrode, leaving rust spots. If the magnets must be plated in. the magnetized condition, all adhering iron or steel should'be removed carefully, and a set ofmagnets had 'best'be placed'in the bath permanently to pick up any particlesof magnetic OIEfBlI'OllS material which might fall into the bath.

If the magnets havea very. rough surface, it. is

considered advisable to plate them with tin, work.

down the coating with a rotary scratch. brush or wire brush, and to apply a coating oftin outside the brushed coating. This process may be repeated several times. The brush utilized should preferably "have brass wires. The usual type of steel wire brush istoo apt to leave small steel particles upon the magnet. These will later cause difliculty when the magnets are plated. The final coating of tin is best made over 1000 of an inch in thickness, and may be made much thicker. An additional-advantage of coating the magnet with tin is that soft soldering may be done directly to'the coating. The usual Alnico magnet material will not, allow such soft soldering.

Althoughv the plating process and products have been disclosed for Alnico magnet material, it is obvious that this'technique may be applied to any other. permanent magnet material where the same problemsappear. It may be applied to any .othermagnet composition which has a large proportion of aluminum, which aluminum tends to ,prevent electroplating by usual methods. Alternatively, it may be applied to any of the other ferrous alloys having aluminum as 'an ingredient.

JIhe possibility.. of soft soldering mentioned above-hasparticular application to magnetic instrument construction. Thus tin-plated magnets maybesoldered to. a holder, which is clamped to orotherwisefastened in adjustable relation to.a.moving system. ofv a compass.

.-Although.the.f-ull. advantages of tin are best gainedby electrolytic deposition as taught herein, .tin may beapplied in other ways, such as by sprayingin themolten form with a metal spray gun. vSuch spray guns make use of a wire of the metal desired to be sprayed. In operation, they melt the wire, which.is..continuously fed into a flame, and by the use of compressed air, spray the molten metal in small particles upon the surface to'be'coated. By holding-such a spraygun .at some'distance from thepiece to be coated and using a fine, spray, it will be possible to obtain a somewhat roughened surface. In most cases,

' pearance of an entirely'newunit, and willnot' this will .not be found as satisfactory as the electrolytic process described herein.

Figure 6 shows the manner of plating the moving assembly shown herein Here 2! is a plating tank within which is contained a plating'solution having a composition such as referred to above in connection with the plating of the mag net. This solution is indicated as 22. Within the solution is an anode 23, of solid tin. Dipping into the solution is a card andfloat assembly 8 such as shown in the assembled view of thecompass in Figure 1. A wire leads the current to this assembly. Fastened to the float assembly with soft solder is a breather tube'24, whose'free opening extends above thelevel of the liquid. Due to the fact that the tin..mu'st .be applied in a warm solution, and that the float assembly must be plated in assembled.conditionto'insure a complete coating, the ordinary platingfltechniques involve the development. of stress-within the float assembly. This assembly isnormally sealed, and when placed into the hot bath, the air containedwithin the float expands and dis torts it. There is thusv introduced. a strain which may cause permanent injury or permanent weakening of the float. Ordinarily, the float assembly is made of thin metal, making this latter process all the more undesirable. By the use of the breather tube,.the interior of'the float is at all times kept at atmospheric pressure. After thepiece has been plated, thesoft soldered connection can be broken between the tube and the float assembly. The opening remaining can then be sealed completely with solder.

If the composition and currentdensity taught hereinare utilized, andif'the proper temperature as taught herein is utilized, it will befound that the'tin will be deposited in crystalline condition. The moving system will thus havea'dull grayish-white appearance, free from glare. This presents a pleasing surface, and one which does not fatigue the eyes in longobservation.

The float and card assembly. may be madeof sheet brass, with the various portions 'spun or die.

show the marred surfaces suggestive of a repaired unit.

After the card assembly-has been plated and after the various small parts, such 'asscrews, magnets, and other removable elements entering into the assembly ofthe card have been placed in their proper positien,-and the card completely assembled, it may be put into the plating bath for-a short time to receive a final coat of tin. Thus, any spot which has been left open by error or from :which the tin has been abraded in handling will be coated and thus-protected from corrosion.

The card andfloat assembly, constituting'the moving system, have been shown in vertical positionzinctheplating bath. It is understood that the "anode maybe of disc-like form, roughly shapedito. conform to .the general contour of :the card-assembly. By this, allparts of the upper surface of the card assembly will be nearlyequidistant from the anode. An auxiliary anode may be placed vertically on the other side of the as sembly so as to cause the effective plating of this side.

When the card assembly has been completely assembled, with the magnets, clips, screws, and other parts, the entire assembly may be placed in the plating bath for a final thin coat of tin. When this is done, it has been found best to allow the assembly to lie in the horizontal position instead of the vertical position as shown in the drawing, and to have the anode lie horizontally beneath the assembly. The magnets will thus be upward and should preferably project out of the liquid. One reason for this is that the magnets are magnetized before being finally assembled, and the proper adjustments made to orient them. They may accidentally pick up small particles of iron, and if immersed in the plating bath, a coating of tin will form over these particles. The particles will later become loose, possibly leaving open spots in the plated coating over the magnet. In any event, they may prevent the brushing off of the particles, resulting in the complete assembly of the instrument with the particles adhering.

Figure 7 shows the plating of the bowl I', together with the attached expansion chamber 4. Here is shown a tank 2|, in which is contained a plating solution 22, of the composition described in connection with the plating of the Alnico material. The bowl I is normally made from a bronze casting. After being machined and after having a recess bored at the lower end, the expansion chamber 4 of thin metal, usually of spun brass, is soldered to the bottom with soft solder. The expansion chamber itself is often made of several members which are joined together with soft solder. The anode 25 shaped like a cylinder with an upstanding portion I2, is placed preferably centrally within the bowl I. By using the current density, composition of bath, and temperature as shown herein, an adherent and crystalline coating of tin will be deposited in the interior surface of the bowl l and in the interior of the expansion chamber 4.

The exceptionally high throwing power of tin will allow it to reach deep into the crevices. Likewise any very small hole in the bowl or expansion chamber will be filled with tin. The coating will also allow easy soldering, should repair be required, since tin forms a very good foundation for soft solder. The same dull finish above referred to will be deposited on the inside of the bowl. This will provide a satisfactory grayish-white surface, which will make for easy reading and the reflection of light within the bowl, without the development of any metallic glare. The surface can be renewed easily, should it be injured, in the same manner as indicated in the discussion of the plating of the card assembly above. However, should it be desired to paint the interior with white paint, the crystalline, or roughened surface will provide a far better foundation for the paint than the smooth surface usually left by hot tinning. In the past, an albumin paint, usually made of egg white and white lead has been used. This has been found to adhere very well to the tin foundation. A better coating is a paint made up of some white pigment such as titanium white in a vehicle such as vinyl resin. Such a coating is impervious to alcohol, is easier to apply than the albumin paint indicated above, and will adhere exceptionally well to the tin undercoating. However, if the paint is omitted, a perfectly satisfactory-surface will result. )7

It is to be noted that the anode 25, is placed within th bowl. It has been thus placed so that the inside of the bowl principally will be coated, although a slight amount of tin will be deposited outside. This outside coating will be of aid in applying any exterior coating, such as the black paint ordinarily applied. If it is desired to have the outside coating heavier, ring shaped anodes may be placed about the bowl and plating conducted inside and outside simultaneously.

While the above process has been indicated for the magnet, moving assembly, and bowl, they may obviously be applied to the small parts which are used in the assembly. Thus, they may be applied to screws, clamps, springs, and any other small removable parts which are used in the compass.

It has been found that the plated coating of tin for the interior of the bowl and for the moving system have great advantages in the operation of the compass. Since in the movement of the moving system within the bowl, the liquid is set in motion, the material having least adhesion to the liquid will be best as a coating. The parts will then adhere less strongly to and be less retarded by the liquid. Although the plated coating has a type of roughness, it is of a microscopic degree, as compared with that which will be noted in paint. The moving system will therefore move with less hindrance through the liquid and the response of the compass will be superior to that of a system in which other materials are employed. Similarly, the liquid moving inside the bowl will move with least hindrance if the bowl is made relatively smooth. The plated coating is smoother than the paint customarily used and there will therefore be less of the type of error known as swirl.

Although the above method has been shown as applied to a compass which employs liquid contained therein, it may obviously be applied to a similar instrument which operates without liquid. Th corrosive fluid in this case would be air, such as salt air, or air containing various corrosive gases, as well as oxygen.

While the plating of metal pieces has been disclosed herein, it will be seen that it is possible to plate non-metallic pieces by the same technique, by coating them with some conducting material. Thus, non-conducting pieces may be coated with graphite or with chemically deposited or "sputtered deposits of metals. The electrolytic tin coating may then be applied over these preliminary coats.

This is a division of applicants Serial No. 402,030, filed July 11, 1941. This parent application has matured into Patent No. 2,361,548.

The scope of the invention is indicated by the appended claim.

We claim:

A method of manufacture of hollow floats of thin metal for ship compasses in which a plating procedure involving immersion of the said float into a hot plating bath is involved, which comprises the steps of forming a float, attaching a breather tube to an opening in said float, then immersing the said float in a plating bath, with the opening of the breather tube exposed to the atmosphere, plating the said float while in said plating bath, removing the said float from the bath, removing the said breather tube, and sealing said opening in the float, the breather tube preventing the setting up of undue strain in the Number Name Date float due to expansion of air therein. 1,906,376 Holmes May 2, 1933 JOSEPH M. S. KAUFMAN. 1,975,818 Work Oct. 9, 1934 SHELLEY KRASNOW. 2,057,762 Boone et al Oct. 2, 1938 JOSEF A. SCHAERFL. 5 2,833,567 Helmore Nov. 2, 1943 OTHER REFERENCES REFERENCES CITED The Metal Industry, Oct. 18, 1929, pages 371, 72

The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Metal Industry, Apr. 1, 1939, pages 161-164.

Electro-Tinning, by S. Baler, in publication N0. 2 of International Tin Research and Development Number Name Date 883,756 Steiner Apr. 7, 1908 Come, 9 pages 3 Journal of the Electiodeposltors Technical 950,777 Wmslow Mar. 1, 1910 1 Society, vol. 12 (1936-37), pages 65-68.

1,560,017 Cleland. et a1 Nov. 3, 1925 10 Technical Publlcatlons of the International Tm l827142 De Trauup 1931 Research and Develo meat Council Series A No 1,904,432 Fink Apr. 18, 1933 p 67 (1937) pages 3-8. 

